Charles Ellicott Commentary Isaiah 45:5

"I am Jehovah, and there is none else; besides me there is no God. I will gird thee, though thou hast not known me;" — Isaiah 45:5 (ASV)

There is no God beside me. — Commonly, the formula is used in antithesis to polytheism. Possibly we may think of it here as in contrast with the dualism of Persia, or, if that is assigned to a later date, of Babylonia.

I girded thee. — The opposite of the “loosing,” or “ungirding,” of Isaiah 45:1, and so implying the idea of giving strength.